A alternative magnetic field generator is prepared by special circuits and active coils and the effects of different magnetic field intensities on the macro morphologies and microstructures of Fe-based composite coatings are studied by laser cladding process. Based on the electromagnetic principle and liquid metal solidification theory, it describes the solidification process of laser cladding coatings and reveals the main mechanism that magnetic field induced columnar dendrites transform into equiaxed crystals. The results show that the skin effect of liquid metal molten pool surface and alternating electromagnetic force allow the solidified cladding layer surface morphology to the wave form. The height of cladding layer and cross-section area decrease with the increase of magnetic field current, but the cladding layer width changes a little. The electromagnetic force in molten pool interior drives the dendrite ablation and mechanical break, and the free broken dendrites become a new nuclei to increase the nucleation rate, by which the top microstructure of cladding layer transforms from dendrite crystals to equiaxed crystals. Furthermore, the equiaxed crystal zone becomes wider with the increase of magnetic field current, but the bottom microstructure has a little change.